A wide variety of IMDs that employ electronic circuitry for providing electrical stimulation of body tissue and/or monitoring a physiologic condition are known in the art. A number of IMDs of various types are known in the art for delivering electrical stimulation therapies to selected body tissue and typically comprise an IPG for generating stimulating therapies and at least one electrical medical lead bearing a stimulation electrode for delivering the stimulating pulses to the selected tissue. For example, cardiac pacemakers and implantable cardioverter-defibrillators (ICDs) have been developed for maintaining a desired heart rate during episodes of bradycardia or for applying cardioversion or defibrillation therapies to the heart upon detection of serious arrhythmias. A wide variety of tissue stimulating IMDs are known for stimulating various nerves, the brain, the GI tract, the cochlea, and various muscles and organs for treating a variety of conditions. Further drug delivery IMDs have been developed to deliver drugs from a reservoir to body organs or structures through drug delivery catheters.
There are at least four paramount considerations or goals that are taken into account in the design and fabrication of such IMDs. First, the IMD operation must be safe, reliable and effective in delivering a therapy and/or monitoring a physiologic condition. Second, the IMD must be long lived and be cost-effective relative to alternative therapies. Third, the IMD must be reasonably miniaturized so that it can be implanted without being uncomfortable and cosmetically distressing to the patient. Finally, each new generation of IMD must satisfy the first three considerations while provide an ever increasing number of performance features and functions that are clinically beneficial to the patient and useful to the medical community.
Electrical medical leads typically comprise a lead body extending between lead proximal and distal ends and comprising one or more electrical conductors and in many cases a lead body lumen extending between the lead proximal and distal ends. One or more electrode and/or sensor are located along the lead body, typically at or near the lead distal end, and are electrically connected to a lead conductor. A lead connector element for each lead conductor is located in a lead connector assembly at the lead body proximal end and is adapted to be coupled to an electrical terminal of the monitor or IPG.
Unipolar, bipolar and multi-polar electrical medical leads have been developed having one, two and three or more, respectively, lead conductors, electrodes/sensor terminals and lead connector elements. Typically, lead connector elements comprise at least a proximal connector pin in unipolar leads and additional, more distally located connector rings in bipolar and multi-polar electrical medical leads that are arrayed in-line, separated by insulator bands, along the length of the lead connector assembly. A proximal lumen end opening is provided in the connector pin of medical electrical leads having lead lumens extending to or through the lead end. Industry wide international standards have been adopted that dictated the diameter and length dimensions and spacing of the connector pin and ring(s). In one typical case, the connector pin has a diameter that is smaller than the connector ring(s), and the connector pin and rings are separated by insulators having outwardly extending sealing rings providing fluid seals comporting with the IS-1 standard.
Implantable monitors and IPGs, as well as implantable drug dispensers, generally have taken the form of a hermetically sealed IMD housing, enclosing a power source and electronic circuitry (and a drug delivery reservoir in the case of drug delivery IMDs), and a connector header or block. For convenience and not by way of limitation, the two parts of all such IMDs that are joined together in use are referred to herein as: (1) an IPG comprising an IPG housing and an IPG connector header; and (2) an electrical medical lead. Electrical feedthroughs extending through the IPG housing couple the electronic circuitry with one or more IPG header connector elements that electrically and mechanically engage the lead connector elements. The electronic circuitry provides stimulation therapies through the electrodes and/or processes signals picked up through the lead-borne electrodes and/or sensors.
The lead connector assembly must be joined with the IPG header in a manner that assures the safety and reliability of the IMD over its lifetime. At present, most IPG headers are formed from biocompatible plastic having one or more elongated bore shaped to snugly receive a lead connector assembly and to establish electrical and mechanical contact between the lead connector elements and respective IPG header connector elements. The bore of the header typically contains one or more annular connector element that engages with a respective one of the connector pin and connector ring(s) located of the proximal lead connector assembly. The engagement has been historically accomplished by tightening a setscrew transverse to the bore of the IPG header connector element so that the setscrew tip securely abuts the lead connector pin or ring extending through the connector element bore as disclosed in commonly assigned U.S. Pat. No. 4,226,244.
The IPG header bore and mating lead connector assembly satisfy an aforementioned international connector standard, e.g., the IS-1 connector standard commonly in use in conjunction with implantable pacemakers and defibrillators, corresponding generally to the connector configurations illustrated in U.S. Pat. Nos. 5,076,270, 5,514,172, and 5,431,695. Various atypical connector assemblies and assembly standards have been proposed, most significantly, dictating common diameters, lengths and spacing between all lead connector elements without any insulating rings extending outward from the insulators, e.g. the mating lead and IPG connector configuration depicted in commonly assigned U.S. Pat. Nos. 5,070,605 and 5,843,141. Numerous other proposals for such multi-polar in-line connector systems have been put forward, as set forth in U.S. Pat. Nos. 4,934,367, 5,304,219, 4,971,057, 6,327,502, and 4,469,104.
The connection standards continue to evolve in order to accommodate an increasing number of electrical connections between lead connector elements and the IMD circuitry within the IPG housing, while maintaining the integrity of the electrical and mechanical connections, providing a seal against ingress of body fluids, simplifying the connection steps, minimizing overall size of the IPG header, and accomplishing all of these goals economically. The number of connections required is increasing in the field of cardioversion/defibrillation and cardiac pacing in order to accommodate upper and lower and right and left heart chamber pacing and cardioversion/defibrillation. There is a long recognized need to be able to provide timed neurological stimulation to four or more separated sites of the spinal cord or nerves to alleviate pain or muscle groups to achieve functional electrical stimulation or the brain to alleviate tremors and the like. In the field of cochlear implants, there is a need to be able to make up to 32 connections as indicated in U.S. Pat. Nos. 6,321,126 and 6,198,169. However, new connector designs are advanced in the '126 and '169 patents that avoid using the widely accepted in-line connector configuration comprising an in-line lead connector assembly and IPG header bore as described above.
Generally, it is desirable to minimize the cross-section of the header bore and the corresponding diameter of the lead connector assembly, space the respective connector elements close together and reduce the minimize the size of the connection and attachment parts. The use of a setscrew to attach each respective lead and IPG connector element together limits the ability reduce overall size. A tripolar, in-line connector configuration and a quadripolar, in-line connector configuration are depicted in commonly assigned U.S. Pat. No. 5,766,042 and in the above-referenced '141 patent, respectively, that seek to maximize the number of connections that can be accomplished in the space allotted to the header without using setscrews. Many component changes have been proposed to eliminate the use of setscrews in favor of header connector elements that are spring-loaded or otherwise act to firmly grip the lead connector elements with friction and compression as the connector assembly is inserted into the IPG header bore as disclosed, for example, in the above-referenced '605 patent and in U.S. Pat. Nos. 5,795,165 and 5,968,082. Cam mechanisms to lock the lead connector assembly into the header bore are also disclosed in the above-referenced '042 and '297 patents, for example.
The above-referenced '141 patent discloses a practical, multi-polar, in-line IPG header and lead connector assembly configuration and a connector system for use in interconnecting the same. Typically, lead connector assemblies are pushed into the header bore until the lead pin is fully seated in the deepest part of the bore and the pin end abuts the bore end. But, the header bore of the '141 patent is open ended such that the lead connector assembly can be pulled through the header bore by a tool extending all the way through the bore and fitted into the lead lumen. Although a setscrew is not shown in the depicted embodiments, a single setscrew could be provided to secure the lead connector assembly once it is pulled through the header bore as suggested in the '141 patent.
The IPG header embodiments disclosed in the '141 patent are formed of a rigid header base having an elongated bore extending through it that is shaped with four aligned recesses that each receive a miniature tubular connector element and insulating fluid seal arranged end-to-end so that they are axially aligned. Each recess is sized so that each set of header connector elements and insulating fluid seals abut one another and bulkheads separating the recesses in order to remain in place under axial load. The lumens of the four sets of connector elements and insulating fluid seals are aligned axially to form the header bore receiving the lead connector assembly. The lumens of the tubular header connector elements are formed with spring elements to frictionally engage the lead connector rings, and the lumens of the tubular fluid seals are formed with inward directed annular sealing rings to engage insulating rings of the lead connector assembly. The metal tubular connector elements are axially rigid, but the elastomeric, electrically insulating, fluid seals are compressible axially and diametrically.
During fabrication, the four sets of header connector elements and insulating fluid seals are inserted into a cavity of the header base such that the bores of the header connector elements and insulating fluid seals are aligned axially to define the header bore when assembly is completed. Electrical conductors extending from the housing supported electrical feedthrough pins are bent over and welded to the exterior surfaces of the tubular connector elements. Elastomeric silicon rubber of epoxy or the like is injected into the base bore to surround and insulate the exposed surfaces of the four sets of header connector elements and insulating fluid seals and the conductors.
While a high degree of miniaturization of the IPG header is achieved, the embodiments disclosed in the '141 patent have proven difficult to assemble and use.
A further in-line implantable medical lead connection system for connecting in-line lead connector assemblies with either IPG headers or lead extension is disclosed in PCT Publication No. WO 00/64535. The IPG header or lead extension connector is formed of a setscrew connector element and a plurality of miniature tubular connector elements and insulating fluid seals arranged end-to-end so that they are axially aligned to form the header bore. Each tubular connector element is formed having an interior channel that traps a continuous coil spring that is wound on an angle that defines and surrounds the connector element bore and that is compressed when contacted by a lead connector element inserted through the connector element bore. Presumably, the elements of the array, as well as a strain relief element, are lined up and held in alignment, perhaps by a mandrel inserted through the aligned bores or an external cage or the like, while the insulative housing of the lead extension or IPG header is molded about the array. Similar uses of trapped continuous coil, IPG connector elements are disclosed in U.S. Pat. Nos. 5,076,270 and 5,336,246.
There remains a need for a miniaturized in-line connector system for IMDs that is simple and inexpensive to fabricate and is reliable in use.